Antifouling paints are used to prevent and delay the fouling of underwater structures (e.g. ships' bottom, docks, fishnets, and buoys) by various marine organisms such as shells, seaweed, and aquatic bacteria. When such marine organisms adhere and propagate on an underwater structure like the bottom of a ship, the surface roughness of the whole ship may be increased to induce decrease of velocity of the ship or increase of fuel consumption. Further, removal of such aquatic organisms from the ship's bottom needs much labour and a long period of working time. In addition, if these organisms adhere and propagate on an underwater structure such as a steel structure they deteriorate their anticorrosive coating films leading to a reducing of the lifetime of the underwater structure.
Underwater structures are therefore coated with antifouling paint employing polymers containing various hydrolysable groups and more specifically organosilyl groups.
EP 0297505 relates to an antifouling paint that contains a polymer having organosilyl groups and/or organopolysiloxane groups in side chains. Since the organopolysiloxane group is derived from dehydrating condensation or like means of silicon oil with methacrylic acid, this patent refers to a mixture of oligomers having different numbers of the recurrence of the organosiloxane group.
Another patent JP 10245451 A describes a mixture of organosilylated carboxylate oligomers having different numbers of the recurrence of the organosiloxane group in acrylic rubber composition.
WO 8402915 and JP 63215780 A describe an antifouling paint of the hydrolysable self-polishing type employing a methacrylic ester polymer having triorganosilyl group in side chains or a similar polymer. Other examples of patents and patent applications related to the use of organosilyl acrylate polymers in antifouling compositions are EP 131626, U.S. Pat. No. 4,593,055, 4,594,365, JP 63118381 A, EP 0775733, WO 9638508, JP 11116257 A, EP 802243, EP 0714957, JP 07018216 A, JP 01132668 A, JP 05077712 A, JP 01146969 A and U.S. Pat. No. 4,957,989 and hereby incorporated by reference.
Some of the polymers used in the above-described antifouling paints are based on silylated carboxylate monomers.
Several processes are known as conventional techniques for the synthesis of said silylated carboxylate monomers.
JP 5306290 A describes a process to obtain a methacrylic functional group-containing organosilicon compound. The process comprises reacting methacrylic acid with a halogenoalkylsilane (e.g. trialkylsilylchloride) in the presence of a tertiary amine compound having a cyclic structure. This process has disadvantages such as the reduced availability and storage stability of the silyl chloride. Moreover, the reaction yields as a by-product a hydrogen halide (which provokes the corrosion of the production equipment) or a halide salt (which has to be removed by filtration).
The synthesis of trimethylsilyl methacrylate from methacrylic acid and hexamethyldisilazane is described in A. Chapman & A. D. Jenkins J. Polym. Sci. Polym. Chem. Edn. vol 15, p. 3075 (1977).
JP 10195084 A discloses the reaction of unsaturated carboxylic acid such as acrylic acid or methacrylic acid with a trialkylsilylhydride compound in the presence of a copper catalyst. One of the disadvantages of this method is the risk of hydrogenation of the unsaturated carboxylic acid due to a side reaction of the produced H2 on the carbon-carbon double bond.
Trialkylsilylcarboxylates of aliphatic carboxylic acids can be obtained by transesterification. H. H. Anderson et al. describe in J. Org. Chem 1716 (1953) the reactions of triethyl silyl acetates with halogenated propionic acids and in J. Org. Chem. 1296 (1954) the reactions of trifluoro silyl acetates or propionates with chloroacetic acid; they distil the acetic or propionic acid under reduced pressure.
Russian chemists (Izv. Akad. Nauk. Ussr. Ser. Khim. 968 (1957)) run similar reactions at much higher temperatures (190–210° C.).
JP 95070152 A discloses reactions of trialkylsilylacetates with C6 to C30 carboxylic acids (e.g. palmitic, myristic, benzoic, . . . ); the acetic acid is distilled under reduced pressure or azeotropically with hexane.
S. Kozuka et al. in Bull. Chem. Soc. Jap. 52 (7) 1950 (1979) study the kinetics of acyloxy exchange reaction between acyloxysilanes and carboxylic acids. The rate of the reaction has been found to proceed faster with a stronger attacking acid and a more basic leaving acyloxy group.
An object of the present invention is to provide a novel process capable of readily preparing organosilylated carboxylate monomers in a high yield from easily available starting materials.
Another object of the present invention is to provide a more direct method for the synthesis of such organosilylated carboxylate monomers, with easy work-up procedures.
A further object of the present invention is to provide a novel process offering an improvement vis-à-vis of the disadvantages disclosed above.
The present invention is based on the use of unsaturated carboxylic acids with acyloxysilanes to synthesize organosilylated carboxylate monomers. The use of unsaturated carboxylic acids in this reaction was unexpected as it is well known by the man of the art that the unsaturated carboxylic acids are polymerisable and lead to very low rate of reaction.
The present inventor has surprisingly found that by reacting acyloxysilanes with unsaturated carboxylic acids weaker than the leaving acyloxy group, organosilylated carboxylate monomers could be synthesised.